1. Field of the Invention
The present invention relates to an electron emission device and an electron emission display device using the same.
2. Description of the Related Art
An FED (Field Emission Display) in field electron emission display apparatuses is known as a planar emission display equipped with an array of cold-cathode electron emission source which does not require cathode heating. For example, the emission principle of an FED using a spindt type cold cathode is in that electrons are drawn out from the cold cathode into a vacuum by the gate electrode located apart from the cold cathode in a similar manner of a CRT (Cathode Ray Tube) which has a cathode different from that of the FED, and then the electrons impinge onto the fluorescent substance that is coated on the transparent anode, thereby causing light emission.
However, this field emission source faces a problem of low production yield because the manufacture of the minute spindt type cold cathode is complex and involves many steps.
There also exists an electron emission device with a metal-insulator-metal (MIM) structure as a planar electron source. This electron emission device with an MIM structure has an aluminum (Al) layer as a cathode, an Al.sub.2 O.sub.3 insulator layer of about 10 nm in film thickness and an Au layer, as an anode, of about 10 nm in film thickness formed in order on the substrate. With this device placed under an opposing electrode in a vacuum, when a voltage is applied between the underlying Al layer and the overlying Au layer and an acceleration voltage is applied to the opposing electrode, some of electrons leap out of the overlying Au layer and reach the opposing electrode. Even the electron emission device with an MIM structure does not yet provide a sufficient amount of emitted electrons. To improve this property of emission, it is considered that there is a necessity to make the Al.sub.2 O.sub.3 insulator layer thinner by about several nanometers and make the quality of the membranous of the Al.sub.2 O.sub.3 insulator layer and the interface between the Al.sub.2 O.sub.3 insulator layer and the overlying Au layer more uniform.
To provide a thinner and more uniform insulator layer, for example, an attempt has been made to control the formation current by using anodization to thereby improve the electron emission characteristic, as in the invention described in Japanese Patent Application kokai No. Hei 7-65710.
However, even such an electron emission device with an MIM structure which is manufactured by this method still ensures a sufficient electron emission property of an emission current of about 1.times.10.sup.-5 A/cm.sup.2 and an electron emission efficiency (emission current/diode current)of about 1.times.10.sup.-3. Since there is a difficulty in the method using anodization the electron emission device is not put to practical use yet. One of the factors influencing the device property of the electron emission device with an MIM structure is the quality and thickness of the insulator layer. It is considered that there is a necessity to make the insulator layer still thinner enough for occurrence of tunnel effect at i.e., about several nanometers in thickness. Therefore, pinholes are apt to appear in the insulator layer, so that the quality of film thereof is spoiled. Further one of the factors influencing the device property of the electron emission device with the MIM structure is the state of interface between the insulator layer and the metal layer. If the surface of the insulator layer after deposition is rough then the contact between the insulator layer and the metal layer becomes poor so as to make the electron emission unstable in the device.